1. Field of the Invention
The present invention relates to an instrument for optically measuring a property of an object by means of photoelectrically receiving the output of a light source transmitted through or reflected by the object, the obtained photoelectric signal being utilized as information concerning the property of the object under inspection.
2. Description of the Prior Art
As an example of an apparatus for optically measuring a property of an object, the densitometer may be mentioned. The densitometer is an instrument for measuring optical density of an object by means of projecting a light toward the object, photoelectrically receiving the light transmitted through, or reflected by the object, and processing the obtained electric signal. In the above signal processing step of the densitometer, some complex device including logarithmic conversion means is generally required since the optical density is defined in relation with the logarithm of the obtained electric signal.
One type of densitometer known in the prior art, and disclosed in Japanese utility model publication No. 48-11347, comprises a circuit means for producing a voltage output which decays from a standard level in an exponential function of time t, means for measuring the light of a light source by way of an object to produce an output of a stationary level commensurate with the measured intensity of light, and means for counting time T between the initiation of decay of the voltage output and the attainment of the stationary level by the decaying voltage output.
In the case of the above densitometer, the circuit means for producing a decaying voltage output corresponds to the logarithmic conversion means.